Soil Compaction Effects

Compaction Process

• The compaction process is assumed not to decrease the volume of solids or soil grains.

Effects of Compaction

• Increases shear strength, density, and bearing capacity of soil.
• Allows for larger loads to be applied to compacted soils due to their increased strength.

Mechanism of Compaction

Cohesive Principles

• Interaction between adsorbed layer and interpretable force.
• Breaking up of old bonds and establishment of new bonds between particles.
• Bending and distortion of soil particles.

Cohesionless Principles

• Rearrangement of soil grains.
• Breaking up of some cementation.
• Bending and distortion of soil particles.

Theories of Compaction

• Lambe theory: physico-chemical concept.
• Proctor theory (1933): lubrication theory, where water addition causes a thin layer to be absorbed by soil grains, increasing the layer with more water.

Role of Water in Compaction

• Water lubricates soil grains (cohesionless soil), allowing them to slide easily and achieve a denser arrangement.
• Water expansion of the double layer, leading to a more orderly arrangement of particles, resulting in higher density (clayey soil).

Phase Diagram

• For a given water content w, the maximum density (ZAV) cannot be reached by compaction.

Soil Compaction

• Objective: increase density, strength, bearing capacity, and reduce permeability and compressibility
• Laboratory work: obtain maximum dry density and optimum water content
• Field compaction: executed by contractors using rollers and compactors

Compaction Process

• Definition: increasing soil unit weight by reducing the soil void ratio using mechanical devices
• Modified Proctor Test: compacting soil in five layers with a 10 Lbs hammer, 18 inches drop height, and 25 blows/layer
• Modified Proctor Energy: 56,250 ft-lb/ft³, calculated by (25 blows/layer) * (5 layers) * (10 lbs) * (1.5 ft) / (1/30) ft³

Comparison of Standard and Modified Proctor Tests

• Mold size: 1/30 ft³ for both tests
• Standard Proctor Test: 12" height of drop, 5.5 lb hammer, 3 layers, 25 blows/layer, and energy 12,375 ft-lb/ft³
• Modified Proctor Test: 18" height of drop, 10 lb hammer, 5 layers, 25 blows/layer, and energy 56,250 ft-lb/ft³

Compaction Procedure in Lab

• Method: removing air voids to achieve a degree of compaction (S=1)
• Water content: wW / vt vw

Soil Compaction

• Objective: Increase density, strength, bearing capacity, and reduce permeability and compressibility
• Laboratory work: Obtain maximum dry density and optimum water content
• Field Compaction: Contractors use rollers and compactors to achieve compaction

Compaction Process

• Definition: Increasing soil unit weight by reducing soil void ratio using mechanical devices
• Reduces permeability and compressibility

Modified Proctor Test

• Similar to Standard Proctor Test with exceptions:
  • Soil compacted in five layers
  • Hammer weight: 10 lbs or 4.54 kg
  • Drop height: 18 inches or 45.72 cm
  • Calculated energy: 56,250 ft-lb/ft³

Standard Proctor Test

• Mold size: 1/30 ft³
• Drop height: 12 inches
• Hammer weight: 5.5 lbs
• 3 layers
• 25 blows/layer
• Energy: 12,375 ft-lb/ft³

Compaction Procedure in Lab

• Method: Drop hammer 25 times onto confined soil
• Soil divided into three lifts, each compacted 25 times
• Done 4-6 times from dry to wet
• Goal: Achieve maximum dry density and optimum water content

History of Modified Proctor Test

• Developed during World War II
• By the U.S.

This quiz covers the effects of soil compaction, including increased shear strength, density, and bearing capacity. It explores how compaction enables larger loads to be applied to soils.